Vehicles, such as automobiles and All Terrain Vehicles (ATVs), are generally powered by an internal combustion engine, and the energy generated by the engine is translated into vehicle movement by a drivetrain (also known as a powertrain). The drivetrain generally includes a transmission coupled to the engine, a driveshaft that is coupled to the transmission, and a mechanism coupled to the driveshaft to rotate the wheels of the vehicle. The drivetrain therefore transfers torque generated by the engine to the wheels of the vehicle via the driveshaft, and the torque transferred by the driveshaft subjects the driveshaft to shearing stress. The greater the torque transferred by the driveshaft, the greater the shearing stress within the driveshaft. When a relatively large amount of torque is transferred by the driveshaft, such as when the vehicle tows a heavy load, the shearing stress could reach a critical value resulting in the failure of the driveshaft. This failure could result in the driveshaft shearing into two or more pieces, which could lead to extensive damage to the vehicle that is costly to repair. Additionally, the vehicle operator could be seriously injured by fragments of the sheared driveshaft or by losing control of the vehicle.
In addition to torsional stress, the driveshaft is also subjected to bending stresses. The driveshaft is an elongated cylindrical rod fixed at its far ends, and any bending of the driveshaft normal to its longitudinal axis leads to tensile and compressive stresses within the driveshaft. Such bending of the driveshaft may occur when the vehicle is operated on uneven surfaces, or when the driveshaft contacts rocks or other objects when operating the vehicle over rugged terrain. These bending stresses can also lead to the failure of the driveshaft, resulting in costly repair and/or injury to the operator.
Therefore, there exists a need for a rotational coupling that will not transfer a torque that is over a predetermined maximum value, while also allowing for longitudinal flexibility to reduce bending stresses within the driveshaft.